A hybrid vehicle's driveline may include an engine, a motor, and a generator. The engine, motor, and generator may be operated at conditions that are based on functions or tables stored in memory and vehicle operating conditions. The functions or tables may include empirically determined desired operating conditions that provide desired fuel economy, performance, and emissions. However, driveline components may age and not perform as expected when operated based on the functions or tables stored in memory. For example, engine friction may decrease over time. Further, electric motor friction may vary over time. If the engine, motor, and generator are operated at conditions based on static parameters stored in memory, powertrain efficiency may degrade.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method, comprising: comparing engine efficiency at a present engine speed to engine efficiency at adjacent high and low engine speed values over a domain of a first function to find a maximum driveline efficiency based on driveline electrical losses and mechanical losses; and adjusting engine and motor speed settings responsive to the comparison.
By updating desired engine and motor speeds in response to driveline efficiency estimates based on engine losses and electrical machine losses, it may be possible to operate a hybrid driveline more efficiently over a hybrid vehicle's life cycle. For example, a vehicle may be initially programmed to operate with an engine speed of 1200 RPM when desired wheel torque is 50 NM. However, as the driveline, including the engine and motor age, it may be more efficient to operate the engine at 1225 RPM for the requested wheel torque. The change in desired engine speed may be attributed to engine deposit formation (e.g., carbon), manufacturing variation, fuel type, and other operating condition variations.
The present description may provide several advantages. Specifically, the approach may improve vehicle efficiency over a vehicle's life cycle. Further, the approach may be implemented in a way that reduces the possibility of disturbing a driver while control parameters are being updated. Further still, the approach allows for updating both engine and electric machine losses.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.